Favia Growth

[this is me]

I just picked up this Favia there is some die off(I got a discount on it). I've been feeding it once every other night. I know the flesh will regrow over the skeleton but do they grow new skeleton, or they grow on a rock.
The reason I asked is favia skeleton is thick, it very impressive if they grow it on their own. Here are the pictures.

Feeding time.

 

[xdusty6920]

its a combination of rock and skeleton. they start to develope on rock but start depositing calcium for thier skeleton very quickly. also when there is favia die off, the polyps will grow over the old skeleton but will form a new skeleton over top of the old.......if that makes sense.